With technical development of mobile devices, a laptop computer that can exhibit a performance corresponding to a desktop computer is provided, and nowadays, there is very high demand for the laptop computer.
The laptop computer has a maximum merit of convenient portability, compared with an existing desktop computer, and one of factors that enable such portability is a battery pack, which is an energy source of the laptop computer.
In general, a battery pack of a laptop computer is configured with a plurality of unit battery cells and a pack case that houses the battery cells, and particularly, as a rechargeable battery that is used for a device such as the laptop computer, a cylindrical battery cell of high power and a large capacity is generally used.
The rechargeable battery is generally classified into a hard pack and an inner pack according to a form of a battery pack that is mounted to a case. Because the hard pack forms a portion of an external form of an external device in which the hard pack is mounted, the hard pack has a merit that may be easily mounted to the external device upon using, but in a state in which a battery cell is housed, a case should be designed according to a kind of a corresponding external device and thus there is a problem that the hard pack is relatively expensive and has less compatibility.
In electronic products such as a laptop computer, consumers request a light weight and a small thickness of the product. Therefore, according to a current trend requiring a thin and light laptop computer, a hard pack that is used for the laptop computer is also formed in a thin thickness.
Accordingly, in order to prevent an appearance failure such as a sink mark and a stress mark that may have because of a characteristic of an injection material constituting a pack case, a basic thickness of the injection material should be maintained to 1 mm. However, such a requirement may operate as a fault factor in a thin thickness of the foregoing battery pack.
Therefore, in order to correspond to a consumer's demand, it is necessary to design a battery pack in a smaller thickness than that in an existing battery pack.